Evolutionary psychiatry, also known as Darwinian psychiatry, is a theoretical approach to psychiatry that aims to explain psychiatric disorders in evolutionary terms. As a branch of the field of evolutionary medicine, it is distinct from the medical practice of psychiatry in its emphasis on providing scientific explanations rather than treatments for mental disorders.
This often concerns questions of ultimate causation. For example, psychiatric genetics may discover genes associated with mental disorders, but evolutionary psychiatry asks why those genes persist in the population. Other core questions in evolutionary psychiatry are why heritable mental disorders are so common, how to distinguish mental function and dysfunction, and whether certain forms of suffering conveyed an adaptive advantage.
Disorders commonly considered are depression, anxiety, schizophrenia, autism, eating disorders, and others. Key explanatory concepts include evolutionary mismatch (when modern environments cause mental health conditions) and the fact that evolution is guided by reproductive success rather than health or wellbeing. Rather than providing an alternative account of the cause of mental disorder, evolutionary psychiatry seeks to integrate findings from traditional schools of psychology and psychiatry such as social psychology, behaviourism, biological psychiatry and psychoanalysis into a holistic account related to evolutionary biology. In this sense, its aims meet the criteria of a Kuhnian paradigm shift.
Evolutionary psychiatry is heavily influenced by evolutionary psychology, but as Abed and St John-Smith wrote in 2016, "Unlike evolutionary psychology, which is a vibrant and thriving sub-discipline of academic psychology with a strong and well-funded research program, evolutionary psychiatry remains the interest of a small number of psychiatrists who are thinly scattered across the world." It has gained increasing institutional recognition in recent years, including the formation of an evolutionary psychiatry special interest group within the Royal College of Psychiatrists and the Section on Evolutionary Psychiatry within the World Psychiatric Association, and has gained traction with the publication of texts aimed at a popular audience such as Good Reasons for Bad Feelings: Insight from the Frontier of Evolutionary Psychiatry by Randolph Nesse.
History The pursuit of evolutionary psychiatry in its modern form can be traced to the late 20th century. Landmark texts include George Williams and Randolph Nesse's Why We Get Sick: The New Science of Darwinian Medicine (which could also be considered as marking the beginning of evolutionary medicine), Evolutionary Psychiatry: A New Beginning by John Price and Anthony Stevens, and others. However, the questions with which evolutionary psychiatry concerns itself have a longer history, for instance being recognised by Julian Huxley and Ernst Mayr in an early paper considering possible evolutionary explanations for what has become known as the 'schizophrenia paradox'.
Concepts applied by modern evolutionary psychiatry to explain mental disorder are also much older than the field in many cases. Psychological suffering as an inevitable, and sometimes useful, part of human existence has long been recognised, and the idea of divine madness pervades ancient societies and religions. Cesare Lombroso, a pioneering psychiatrist, began utilising evolutionary theory to explain mental disorder as early as 1864, proposing that insanity was the price of genius, as human brains had not evolved with the capacity to become hyper-intelligent and creative and yet remain sane. Darwin applied evolutionary theory to explain psychological traits and emotions, and recognised the usefulness of studying mental disorders in pursuit of understanding natural psychological function. Freud was heavily influenced by Darwinian theory, and towards the end of his life recommended psychoanalysts should study evolutionary theory. Bowlby's attachment theory was developed in explicit reference to evolutionary theory.
Evolutionary Psychiatry Special Interest Group (EPSIG) In 2016, the Evolutionary Psychiatry Special Interest Group (EPSIG) was set up in the Royal College of Psychiatrists, UK by Riadh Abed and Paul St-John Smith. It is now the largest global institution for connecting psychiatrists and researchers interested in evolutionary psychiatry, with over 1700 members. It has run several seminars and meetings dedicated to evolutionary psychiatry, hosting lectures by prominent academics such as Simon Baron-Cohen and Robin Dunbar. All of the meetings are available on the EPSIGUK YouTube channel. EPSIG also publishes regular newsletters, organises conferences, conducts interviews, and hosts special essays related to evolutionary psychiatry (for which there is not yet a dedicated academic journal). As Riadh Abed (previous chair) stated in a newsletter, "Our aims are both big and radical: they are for evolution to be accepted as the overarching framework for psychiatry and for evolution to take center stage in our understanding of mental health and mental disorder."
Abed and St-John Smith edited a 2022 volume Evolutionary Psychiatry: Current Perspectives on Evolution and Mental Health, co-published by the Royal College of Psychiatrists and Cambridge University Press, marking the most extensive publication in the field to date, and forming the basis for the first podcast dedicated to evolutionary psychiatry, the 'Evolving Psychiatry' podcast.
Psychological function and dysfunction Mental disorders are often defined by 'dysfunction' in psychiatric manuals such as the DSM, without a precise definition of what constitutes dysfunction, allowing any mental state deemed socially unacceptable (such as homosexuality) to be considered dysfunctional, and thus a mental disorder.
Adam Hunt argues that evolutionary theory is uniquely placed to be able to distinguish biological function from dysfunction by evolutionary processes. Unlike the objects and processes of physics and chemistry, which cannot strictly be said to be functioning nor dysfunctioning, biological systems are the products of evolution by natural selection, and so their 'function' and 'dysfunction' can be related to that evolutionary process. The concept of evolutionary function is tied to the reproductive success brought about by phenotypes which caused genes to be propagated. Eyes evolved to see – the function of the eyes is to see – so dysfunctional eyes are those that cannot see. This sense of function is defined by the evolutionary history of eyesight providing reproductive success, not current cultural opinions of normality and abnormality on which common conceptions of health and disorder often depend. Jerome Wakefield's influential 'Harmful Dysfunction' definition of disorder utilises evolutionarily selected effects to ground the concept of 'dysfunction' in the objective process of evolution. Wakefield proposes that mental disorder must be both harmful, in a value-defined sense, and dysfunctional, in an evolutionary sense.
This grounding of dysfunction in an objective historical process is important in the context of psychiatry's history of labelling socially undesirable mental states and traits as 'disorders', such as female masturbation and homosexuality. Current diagnostic manuals are decided by consensus. For example, in 1973 the APA called a vote to reconsider homosexuality's status as a mental disorder. By a 58% majority, it was struck off. The category of borderline personality disorder was created upon the basis of a single paper and consensus between about a dozen psychiatrists. In 2014 psychiatrists voted on the features of a new disorder, internet gaming disorder. Psychiatry's reliance on votes and expert consensus rather than objective evidence or biomarkers has been the subject of longstanding criticism, which evolutionary psychiatry can avoid by adopting the evolutionary definition of dysfunction.
Evolutionary causation and Tinbergen's four questions
The research questions and concerns of evolutionary medicine and psychiatry can be distinguished from normal biomedicine and biological-psychiatry research as asking ultimate instead of proximate questions. This ultimate-proximate distinction was introduced by Ernst Mayr to identify different levels of causational explanation: proximate explanations refer to mechanistic biological processes (e.g. genes, ontogenetic development, hormones, neurological structure and function) whilst ultimate explanations ask about the evolutionary process of natural selection which led to these biological structures and processes functioning as observed. This could be conceived of as proximate explanations are 'how' questions whilst ultimate explanations are 'why' questions.
Niko Tinbergen further deconstructed this ultimate-proximate distinction into his 'four questions'. These questions of mechanism, ontogeny, function and phylogeny can be asked of any single trait or disorder (often behavioural, although not necessarily) to identify the different questions of causation which are simultaneously relevant.
Proximate questions can be separated into questions of mechanism, which concerns how the trait works, the structure and process of its biological mechanism, and questions of ontogeny or individual development which concerns how the trait develops in an individual. Ultimate questions can be either of or evolutionary function or adaptive value, which concerns how the trait influenced fitness throughout evolutionary history; and questions of phylogeny or evolution, which concern the history of a trait down the phylogenetic tree. To take the example of depression, we can ask about proximate mechanisms (e.g., neurotransmitter properties), ontogenetic development (e.g., neurological development over an individual's lifespan), adaptive function (e.g., low mood system) and phylogeny (e.g., apparent low mood in reaction to social defeat in primates).
Key explanatory concepts in evolutionary psychiatry Mental disorder results from many different environmental and genetic causes, with various complex neurological correlates – but evolutionary medicine recognises several general principles which allow vulnerability to disorder. Adapted from Nesse (2019), Stearns (2016) and Gluckman (2016).
Reproductive success over health Natural selection acts on reproductive fitness, not biological states which are what may be considered healthy; healthy states are only selected if they also have positive effects on reproductive success. This is used in evolutionary medicine to explain aging and diseases of senescence: diseases which appear past reproductive age have minimal effect on fecundity. Psychological suffering and various cognitive states which may seem unhealthy or disorderly may equally be products of evolutionary processes if they increased reproductive success. Evidence of this may be seen in disorders associated with substantial apparent dysfunction, yet average levels of fertility.
Mismatch Evolutionary mismatch occurs when evolved traits become maladaptive due to changes in the environment. This is a common factor causing evolutionary change (e.g. in the peppered moth) and is relevant to medicine when the mismatched traits cause problems affecting health. Psychiatric conditions may in some cases be evolved states which we are misinterpreting as disorders because they no longer fit our social expectations; or they may be mental states or traits which would manifest healthily in ancestral environments, but become pathological due to some feature of modern environments. Evidence of mismatch is most prominent when comparing traditional-living humans to modern-living humans or when new environmental factors arise which clearly cause disease (e.g. the availability of cheap, high calorie foods causing obesity).
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